Organic electroluminescent (EL) devices are expected to see practical application in such fields as displays and lighting, and so a variety of research has been carried out recently on materials and device structures with the aim of achieving such properties as low-voltage driving, high brightness and longevity.
A plurality of functional thin-films are used in organic EL devices to increase the performance of such devices. Of these films, a hole injection layer or a hole-transporting layer is responsible for transferring charge between an anode and an emissive layer, and thus serves an important function in lowering the driving voltage and increasing the brightness of organic EL devices.
Processes for forming the hole injection layer or hole-transporting layer are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. On comparing these processes, wet processes are better able to efficiently produce thin-films having a high flatness over a large surface area and therefore are often used particularly in the field of displays.
Given the desire today for enhanced organic EL device performance, improvements in the wet process materials for hole injection layers or hole-transporting layers are constantly being sought. In particular, because they can help improve the brightness characteristics or longevity characteristics of organic EL devices, there is a growing desire for materials which provide charge-transporting thin-films of excellent flatness.